Many of the analytical and diagnostic tests currently being performed require the use of a photometer to measure light or radiation being absorbed, scattered or emitted from a sample cell. The analyte to be measured or tested is either deposited in a discrete sample cell, cuvette, or passed through a sample cell of the flow type in which a continuous flow of liquid to be analyzed is passed. The physical properties of the sample that are typically measured are the absorbance of light passing through the cell, the reduction of light passing through the cell due to scatter caused by particles within the cell, the ninety degree light scattered from a source by particles within a cell (nephelometric) or finally the materials within the cell that fluoresce when excited by a proper exciting radiation.
Various photometers have been developed to measure one or sometimes two of the above noted physical properties. This typically necessitates the use of several photometers in order to perform all of these measurements. With the increasing number of analytical and diagnostic tests now available this need of measuring all of the above properties of a sample analyte has become more of a necessity than previously. This has increased significantly the cost of performing such analysis and has created the need for a low cost photometer capable of performing all of these four functions.
It is also required that the various measurements of the physical properties of the analyte in a sample cell be made with a high degree of sensitivity. In addition it is desirable to be able to subject the analyte to a single wavelength of light, to multiwavelengths of light for some of the more difficult chemistries used in an analysis as well as to make bichromatic wavelength measurements. An additional factor which must be considered is that of straylight rejection. This is particularly true when the fluorescent light emitted by the sample is to be measured. Typically, fluorescent light emitted is of a low intensity and hence much more subject to interference by straylight, particularly by the straylight from the exciting radiation which creates the fluorescence in the first place. Most of these factors may be summarized under the name of detection flexibility i.e., the photometer must have a high degree of flexibility and be able to detect various wavelengths of light.
While there have been many photometers developed in the prior art most of these are not able to measure all oft he four physical criteria set forth above. For example, U.S. Pat. No. 4,060,327 issued Nov. 29, 1977 to International Business Machines Corporation passes light, admitted through an entrance slit, through a sample cell and thence to a pair of gratings which disperse the light admitted through the slit into two separate dispersed beams. The separate beams are then focused on linear arrays of photodiodes providing outputs proportional to the intensity of the light rays at the different wavelengths received thereby. While this system operates across a relatively wide band of radiant energy it is capable only of absorbance and turbidimetric measurements.
Another photometer system is described in U.S. Pat. No. 4,426,154 issued Jan. 17, 1984 to Wetzlar. Wetzlar describes a photometer for measuring fluorescent light, scattered light and/or absorbed light; it cannot measure nephelometric light. Furthermore, the system does not appear to have an effective means of removing straylight from that impinging upon the various photodetectors. Baker Instruments has just announced the introduction of a chemistry system featuring optics enabling it to operate in both absorbance and fluorescence modes. It uses a 180.degree. optical system, apparently like Wetzlar, and is said to include discrete excitation and emission filters. The discrete filters reduce the straylight effects that often occur in a monochrometer. It does not appear capable of nephelometric measurement.
It should be noted that these prior art patents which are typical of all the prior art are limited in sensitivity, versatility and tend to be relatively costly in requiring plural photometers in order to measure all four physical parameters of an analyte, i.e. absorbance, turbidimetry, fluorescence and nephelometry.